Electrical switching apparatus with adjustable deadband

ABSTRACT

Electric switching apparatus having an adjustable differential switching action. A two-state switching device, for instance a relay, assumes a state dependent on the response of a pair of photoelectric cells which, in dependence on the position of a movable vane, are illuminated by a lamp. The switching device is controlled by the cells through a circuit having a switching differential, that is exhibiting hysteresis or backlash, such that switching occurs only when both cells become shielded from the light or exposed to it. The two cells are movably mounted such that the distance the vane has to move to produce switching, and hence the differential switching action, is adjustable.

United-States Patent .Sharp et al. A

[451 Sept. 5, 1972 [54] ELECTRICAL SWITCHING APPARATUS WITH ADJUSTABLE DEADBAND [72] Inventors: Alexander Sharp, Wishaw; Donald William Allan, Hamilton, both of v Scotland [73] Assignee; Honeywell Inc., Minneapolis,

Minn.

[22] Filed: Dec. 1, 1970 [21] Appl. No.: 94,916

' [30] Foreign Application Priority Data Dec. 4, 1969 Great Britain ..59,308/69 [52] US. Cl ..250/209, 250/231 R, 315/159,

[51] Int. Cl. ..G01d 5/34 [58] Field of Search ..317/127; 250/231, 229, 209;

[56] References Cited UNITED STATES PATENTS 3,332,014 7/1967 Orths et al. ..250/231 R 3,596,178 7/1971 Sklyaruk et a1. ..250/231 R Primary Examiner-Ronald L. Wibert Assistant Examiner-Orville B. Chew, II Attorney-Arthur H. Swanson and Lockwood D. Burton [57] ABSTRACT Electric switching apparatus having an adjustable differential switching action. A ,two state switching device, for instance a relay, assumes a state dependent on the response of a pair of photoelectric cells which,

- in dependence on the position of a movable vane, are

illuminated by a lamp. The switching device is controlled by the cells through a circuit having a switching differential, that is exhibiting hysteresis or backlash, such that switching occurs only when both cells become shielded from the light or exposed to it. The two cells are movably mounted such that the distance the vane has to move to' produce switching, and hence the differential switching action, is adjustable.

8 Claims, 5 Figures ADJUSTABLE DEADBAND This invention relates to electric switching apparatus and is particularly concerned with the provision of such apparatus having a switching differential, that is a hysteresis or backlash, also known as deadband which is adjustable over a fairly wide range.

According to the invention electric switching apparatus comprises a holder for a lamp, a relatively movable control member which in one relative position interrupts the path of radiation passing from the lamp to one of a pair of photo-sensitive sensors and in another relative position interrupts the paths of radiation passing from the lamp to both sensors, the sensors being movably mounted such as to permit adjustment of the distance between the two positions, and a two state switching device so controlled by the sensors that switching occurs when both paths become interrupted and when both paths become uninterrupted, the apparatus as a result having a switching differential, that is a hysteresis or backlash, which due to the movable mounting of the sensors, is adjustable. This adjustment may be over a fairly wide range. In consequence the apparatus is particularly suited for control applications where the position of the control member is dependent on the process variable being controlled. In such applications if the switching differential is not fairly large, the contacts of the contactor or other control device controlled by the switching apparatus may chatter.

The pair of photosensitive sensors may be together pivoted about an axis which is at least substantially parallel to the two paths of radiation and is at least substantially perpendicular to the direction of relative movement of the control member. In such a construc tion the control member, for instance in the form of a vane, may be pivotally mounted about an axis which is parallel to but offset from the pivotal axis of the sensors.

By way of example electric switching apparatus in accordance with the invention will now be described with reference to the accompanying drawings in which:

FIG. 1 is a plan view of the apparatus;

FIG. 2 is a perspective view of the lamp and photoelectric cell mounting;

FIGS. 3a and 3b are plan views corresponding to FIG. 1 but with part of the cell mounting removed, showing the manner of operation of the mechanical portion of the apparatus; and

FIG. 4 is an electrical circuit diagram of the apparatus.

Referring first to FIG. 1, the apparatus includes a metal case 1 which contains two printed circuit boards and internal wiring. A mains-voltage transformer 2 is mounted on one end of the case 1 and a plug-in electromechanical relay 3 is mounted on the other end. A two position selector switch 4 is located on the face of the case. The purpose of these components is described later in connection with FIG. 4.

The control member of the apparatus is in the form of alight-weight vane 5 which is pivoted at 6 to the case 1 and is connected by a mechanical linkage 7 to an actuating element, for example the pen of a recording instrument. Thus, movement of the actuating element causes corresponding pivoting of the vane 5 about its axis 6. Such pivoting movement in a clockwise sense from the position shown in FIG. 1 interrupts the beams of light produced by a lamp and incident on the two photoelectric cells. The lamp and cells are carried by a housing 8 which is pivoted at 9 (midway between the cells) to the case 1. It can be seen that the housing 8 and the vane 5 therefore pivot about parallel but offset axes. The housing 8 may be locked in any desired angular position, which is indicated on a calibrated scale 10,

bymeans of a locking screw 11. FIG. 2 shows the arrangement of the lamp, designated 12 and located in a holder 13, and the photo-electric cells, designated 14 and 15. Part of the vane 5 is also visible.

The manner of operation of the mechanical part of the apparatus just described becomes clearer on reference to FIGS. 3a and 3a.

In FIG. 3a, the housing 8 containing the lamp 12 and the photo-electric cells 14 and 15 is in its furthest clockwise position. The vane 5 is so shaped that with the housing in this position the edge 16 of the vane, when the vane is in the angular position shown, is substantially parallel to a straight line 17 extending through the light sensitive areas of the cells 14 and 15. Accordingly on clockwise pivoting of the vane 5 from the position shown in FIG. 3a, the respective beams of light incident on the cells are interrupted almost simultaneously; conversely on subsequent anti-clockwise pivoting both cells are exposed to the beams almost simultaneously. In consequence other than over a very small angular range, as shown by the lines 17, 17' and for example of the order of 0.0065 radians, the two cells are always in the same state, that is they both produce outputs indicative of the presence or absence of incident light. As will become clearer later, the result is that the apparatus has a small switching differential.

In FIG. 3b, the housing 8 containing the lamp 12 and the photoelectric cells 14 and 15 is in its furthest anticlockwise position. Accordingly on clockwise pivoting of the vane 5 from the position shown in FIG. 3b, the beam of light incident on the cell 14 is interruptedby the vane when the latter is in a more anti-clockwise or earlier position, as shown by the line 18, compared to FIG. 3a, while the beam of light incident on the cell 15 is interrupted by the vane when the latter is in a more clockwise or later position 18. Conversely on subsequent anticlockwise pivoting of the vane the cell 14 is not exposed to the beam until the vane has pivoted back to the position 18, that is through a larger angle compared to FIG. 3a. Accordingly the cells 14 and 15 are in different states over a much larger angular range, for example of the order of 0.05 radians. This results in a relatively large switching differential.

Clearly the housing 8 together with the lamp 12 and I the photoelectric cells 14 and 15 can be locked by the locking screw 11 in any position between the extreme positions shown in FIGS. 3a and 3b. Accordingly the switching difierential is infinitely adjustable over the range defined by the two extreme positions.

Reference should now be made to FIG. 4 showing the electrical circuit diagram of the apparatus. The circuit is energized with 240 volts A.C. which is applied across input terminals 20 and therefore across the primary winding of the transformer 2. The reduced voltage which is obtained across the center-tapped secondary winding is full-wave rectified by two diodes 21 and smoothed by capacitors 22 and 23 and a resistor 24.

The resulting DC. is used to energize a voltage stabilizing circuit incorporating two transistors 25 and 26. This circuit provides a stabilized voltage for the lamp 12. The voltagecan be adjusted by means of a rheostat 27. Diodes 28 and 29 provide a temperature compensating reference for setting the lamp current. The DC. also energizes a voltage stabilizing circuit incorporating two transistors 30 and 31. This provides a stabilized voltage for the photoelectric cells 14 and 15 and for a type of Schmitt trigger circuit incorporating two transistors 32 and 33. A diode 34 compensates for temperature variations. The transistor 33 controls a transistor 35 which in turn controls the relay 3 previously mentioned and hence its movable contact which is designated 36.

The two position selector switch 4 shown in FIG. 1 is also shown in FIG. 4. In the following description of the manner of operation of the circuit, this switch 4 is assumed to be in the position shown in FIG. 4.

If both cells 14 and 15 are exposed to light from the lamp 12, i.e. the vane is in the anti-clockwise position as shown in FIGS. 3a and 3b, the signal applied to the base of the transistor 32 renders this transistor conductive. In consequence the transistor 33 is rendered nonconductive and hence the transistor 35 is rendered conductive. The coil of the relay 3 is therefore energized and the relay contact 36 is closed.

If the vane is now pivotted in a clockwise direction, it interrupts the beam of light incident on the cell 14. In consequence the signal applied to the base of the transistor 32 falls to a new level which is arranged to be just above that at which this transistor becomes nonconductive. Accordingly the relay contacts 36 remain closed. After further pivotting of the vane, the beam of light incident on the cell is interrupted. In consequence the transistor 32 now becomes non-conductive, the transistor 33 becomes conductive and the transistor 35 non-conductive. Accordingly the coil of the relay 3 is de-energized and the contacts 36 open.

If the vane 5 is now pivotted in an anti-clockwise direction, it first exposes the cell 15 to an incident beam. The signal on the base of the transistor 32 therefore rises. However due to the hysteresis or backlash ef fect of the circuit the transistor 32 is not rendered conductive. This only occurs when the voltage rises further and it only does this when the vane also exposes the cell 14 to its incident beam. At that instant the transistor 32 starts conducting and hence the relay contacts 36 close.

Accordingly the apparatus provides differential switching of the relay contacts 36 in dependence on the position of the vane 5. The magnitude of the differential action is controlled by pivoting movement of the housing 8.

If the selector switch 4 is moved to its alternative position, the cell 15 is shortcircuited. In consequence the relay 3 is dependent on the output of the cell 14 alone. Thus the apparatus then has a much smaller, non-adjustable, differential switching action.

We claim:

1. Electric switching apparatus comprising support means, lamp-holder means carried by said support means, a pair of photosensitive sensors movably 6 mounted on said support means, a support member, said control member in one position interrupting the passage of radiation from a lamp in said lamp-holder means to one of said photosensitive sensors and in another position interrupting the passage of radiation from said lamp to both of said photosensitive sensors, said movable mounting of said sensors permitting adjustment of the distance between the two said positions, said sensors being together pivoted about an axis which lies substantially in the plane defined by the paths followed by radiation passing from the lamp to the sensors and which is at least substantially perpendicular to the direction of movement of said control member, and a two state switching device so controlled by said sensors that switching occurs when both sensors become shielded against the radiation and when both sensors become exposed to the radiation, said apparatus as a result having a switching differential which, due to the movable mounting of said sensors, is adjustable.

2. Electric switching apparatus comprising support means, lamp-holder means carried by said support means, a pair of photosensitive sensors pivoted on said support means, a control member pivoted on said support means about an axis parallel to but offset from pivoting axis of said sensors, said control member in one position interrupting the passage of radiation from a lamp in said lamp-holder means to one of said photosensitive sensors and in another position interrupting the passage of radiation from said lamp to both of said photosensitive sensors, said pivoting of said sensors permitting adjustment of the distance between the two said positions, and a two state Schmitt trigger-like switching device so controlled by said sensors that switching occurs when both sensors become shielded against the radiation and when both sensors become exposed to the radiation, said apparatus as a result having a switching differential which, due to the movable mounting of said sensors, is adjustable.

3. An electric switching apparatus comprising:

a mp

a pair of photo-responsive sensors,

a movable control member which is movable about an axis in response to an applied control signal and is mounted between said lamp and said pair of photoresponsive sensors for selectively interrupting paths of radiation from said lamp to said pair of photo-responsive sensors,

said photo-responsive sensors being mounted upon selectively adjustable means for changing the relative displacement of said sensors with respect to the angular movement of said movable control member,

switching means connected to said sensors,

said switching means having deadband means controlled by said sensors such that switching occurs when both of said radiation paths become interrupted and when both of said radiation paths cease being interrupted.

4. The invention as set forth in claim-3 wherein:

said selectively adjustable means includes pivotal means for pivoting, with respect to said movable member, said pair of photo-responsive sensors about an axis of said pivotal means.

5. The invention as set forth in claim 4 wherein:

said movable control member which is selectively adjustable includes means for pivoting said movable control member about an axis which is parallel to said axis of said selectively adjustable means.

said movable control member which is selectively adjustable includes pivotal means for pivoting said movable control member about an axis which is parallel to said axis of said pivotal means of said selectively adjustable means, and

said deadband means of said switching means includes a Schmitt trigger type circuit whereby said Schmitt trigger-type circuit senses whether I neither, one or both of said pair of photo-sensitive sensors is conductive. 

1. Electric switching apparatus comprising support means, lampholder means carried by said support means, a pair of photosensitive sensors movably mounted on said support means, a support member, said control member in one position interrupting the passage of radiation from a lamp in said lamp-holder means to one of said photosensitive sensors and in another position interrupting the passage of radiation from said lamp to both of said photosensitive sensors, said movable mounting of said sensors permitting adjustment of the distance between the two said positions, said sensors being together pivoted about an axis which lies substantially in the plane defined by the paths followed by radiation passing from the lamp to the sensors and which is at least substantially perpendicular to thE direction of movement of said control member, and a two state switching device so controlled by said sensors that switching occurs when both sensors become shielded against the radiation and when both sensors become exposed to the radiation, said apparatus as a result having a switching differential which, due to the movable mounting of said sensors, is adjustable.
 2. Electric switching apparatus comprising support means, lamp-holder means carried by said support means, a pair of photosensitive sensors pivoted on said support means, a control member pivoted on said support means about an axis parallel to but offset from pivoting axis of said sensors, said control member in one position interrupting the passage of radiation from a lamp in said lamp-holder means to one of said photosensitive sensors and in another position interrupting the passage of radiation from said lamp to both of said photosensitive sensors, said pivoting of said sensors permitting adjustment of the distance between the two said positions, and a two state Schmitt trigger-like switching device so controlled by said sensors that switching occurs when both sensors become shielded against the radiation and when both sensors become exposed to the radiation, said apparatus as a result having a switching differential which, due to the movable mounting of said sensors, is adjustable.
 3. An electric switching apparatus comprising: a lamp, a pair of photo-responsive sensors, a movable control member which is movable about an axis in response to an applied control signal and is mounted between said lamp and said pair of photo-responsive sensors for selectively interrupting paths of radiation from said lamp to said pair of photo-responsive sensors, said photo-responsive sensors being mounted upon selectively adjustable means for changing the relative displacement of said sensors with respect to the angular movement of said movable control member, switching means connected to said sensors, said switching means having deadband means controlled by said sensors such that switching occurs when both of said radiation paths become interrupted and when both of said radiation paths cease being interrupted.
 4. The invention as set forth in claim 3 wherein: said selectively adjustable means includes pivotal means for pivoting, with respect to said movable member, said pair of photo-responsive sensors about an axis of said pivotal means.
 5. The invention as set forth in claim 4 wherein: said movable control member which is selectively adjustable includes means for pivoting said movable control member about an axis which is parallel to said axis of said selectively adjustable means.
 6. The invention as set forth in claim 4 wherein: said deadband means of said switching means includes a Schmitt trigger-type circuit whereby said Schmitt trigger-type circuit senses whether neither, one or both of said pair of photo-sensors is conductive.
 7. The invention as set forth in claim 4 wherein: said adjustable means includes a housing for mounting said lamp such that said pair of photo-responsive sensors and said lamp are pivoted about said axis of said pivotal means.
 8. The invention as set forth in claim 7 wherein: said movable control member which is selectively adjustable includes pivotal means for pivoting said movable control member about an axis which is parallel to said axis of said pivotal means of said selectively adjustable means, and said deadband means of said switching means includes a Schmitt trigger type circuit whereby said Schmitt trigger-type circuit senses whether neither, one or both of said pair of photo-sensitive sensors is conductive. 